


What if I told you...

by bluefallenfandomwallflowers



Category: Supernatural
Genre: Alternate Universe - Canon Divergence, Angst with a Happy Ending, Casifer, Coda, Inside Cas' Head, Lucifer Possessing Castiel, Lucifer pretending to be Cas, Lustiel - Freeform, M/M, Post-Episode: s11e14 The Vessel, my spin on things
Language: English
Status: Completed
Published: 2016-02-28
Updated: 2016-02-28
Packaged: 2018-05-23 20:27:52
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,237
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6129085
Author URL: https://archiveofourown.org/users/bluefallenfandomwallflowers/pseuds/bluefallenfandomwallflowers
Summary: <blockquote class="userstuff">
              <p>Castiel is stuck inside his own head, forced to watch Lucifer escapade across the world using his vessel for his own selfish deeds.<br/>He deals with it without too much protest, knowing that this is the only way to save the world.<br/>But when Lucifer brings Dean into the picture, you can be certain that Cas won't sit back quietly.</p>
            </blockquote>





	What if I told you...

**Author's Note:**

> Hello!  
> Just a quick little oneshot I wrote after watching The Vessel. I never got around to posting it though so it is a bit late, but I just had a random idea that I decided to put to the keyboard.  
> Hope you like it!

“You know, Castiel… I think this may be my best idea ever.”

Cas looks up at Lucifer, narrowing his eyes and trying to keep his mouth shut. Lucifer sits upon a black throne in the dream, the room dark and low-lit, the walls a blood red. There are books tucked away in bone bookshelves, made of dried skin and blood and Cas tries not to whimper at the sight of broken flesh and fearful souls living in the pages.

They are in Cas’ head, in their shared vessel, hidden deep in the part of Cas’ mind that is neither conscious nor unconscious. They are both simply there and Lucifer has a smug look on his old vessel’s face, a fist folded under his chin. He stares at Cas, his eyes admiring the clothes he had forced Cas into, the linen pants and gray t-shirt, the pale collar bone sliding under the fabric and the cuts on his cheeks. Cas’ wrists and ankles are adorned in shackles and his head is beset with a crown similar to the one Jesus Christ was forced to wear over 2,000 years ago.

It’s a sick joke and it is no surprise that Lucifer finds humor in it.

Cas doesn’t say anything, keeping himself firmly planted on the wooden chair Lucifer told him to sit on, trying to avoid his dark gaze. “Are you afraid of me, Castiel?” Lucifer asks after he gets no answer.

“No,” Cas says.

Lucifer tuts, leaning forward. “You should be, brother. Because when I take out our silly little aunt and her darkness, the world will fall right into my hands.”

“The Winchester’s will not let that happen,” Cas retorts, lifting his chin to try and look brave, like he’s not trembling from the thought of the devil taking over the earth and corrupting and twisting it into a deeper and darker state than it is already in.

Then Lucifer laughs, standing up, putting his hands on his knees like it’s the most hilarious thing in the whole universe, but Cas isn’t laughing. “Oh, Castiel… You humor me.”

He hops off of the top step, landing in front of Cas lightly, hands behind his back. “You have too much faith in those two.”

“They already defeated you once.”

Lucifer sighs, eyebrows scrunching in fake sympathy. He grips the arms of Cas’ chair, leaning in close with a frown. “Well they didn’t exactly do a very good job, did they?”

Cas leans away, turning his head to the side and squeezing his eyes shut. He stills as Lucifer leans closer, his breath deceivingly warm on Cas’ neck and he shivers. “There’s a reason you haven’t cast me out, Castiel,” he says lowly, drawing nearer, too near. “You have faith in me, despite what you think you want to believe. You want me to save your boyfriend and his brother and this broken, little world that our Father created all those years ago. And look at it now, Castiel! It’s just as corrupt as Heaven above.”

Lucifer stands up again, crossing his arms in a contemplative manner, smiling wretchedly. “And I think I might take that for myself too.”

Cas shudders and hangs his head low, feeling the icy tendrils of Lucifer’s grace caress his maliciously, taunting his own with depraved laughs and promises. “We are going to be stuck in here for a while, Castiel,” Lucifer taunts, leaning close again. “So I suggest you get comfy.”

*****

Cas is sitting in his chair, staring at the empty throne before him. Lucifer locked him inside of this horrid room, leaving him to stare at images of death and screaming women and empty eyes while the devil wrapped the Winchesters around his finger, pretending to be Cas.

He catches a few phrases here and there, hearing deep throated Deans and quiet, evil laughs and it bothers Cas, knowing that Lucifer’s façade had not been figured out yet. Sometimes Lucifer would pick at Cas’ mind, taking out any past memories and actions that can fit his evil purpose, helping him dig deeper into the costume and deceit.

Cas sits in pain, enduring the depravity of his vessel trying to hold two angels inside at once. With Lucifer’s archangelic power, they both stay intact, but Cas knows that he could be blown into oblivion if Lucifer got bored. Every time Cas tugs at the chains keeping him in place, Lucifer wraps a fiery thread of grace around Cas’ and immediately he lets go, collapsing in the chair and breathing hard.

There was just no use in trying to escape. So Cas decides that it is safe enough to venture into his thoughts and feelings and memories.

To freely let his mind think about Dean.

He wonders how the hunter will figure it out. Lucifer made the mistake of treating Dean like an object, placing his hand on the wrong shoulder and uttering words that Cas would never say, let alone think. That most definitely had sparked up some sort of suspicion in Dean’s mind. And Lucifer was getting more careless as he spoke, his voice much too gruff after his stern talk with Crowley in Hell, his actions a little too carefree and loose.

Cas lets a laugh roll off his tongue when Lucifer bounces off the hull of the German ship, both of them sinking into the indigo depths of the ocean, Cas jangling free of a shackle while Lucifer teleports, cursing and trying to get situated again.

But Cas’ left hand is free and he tucks it away and doesn’t move again, waiting for the right moment.

*****

Lucifer is slipping up.

Cas feels his agitation from leaving the Hand of God in the hands of Dean Winchester, his annoyance with Sam and his careful research and patience. Lucifer is almost angry at how calm Sam is, how he isn’t going to just **leave the damn kid on the boat** , as he thinks to himself and Cas, and call it a day.

And when Lucifer decides to go ahead and perform the archangel spell without telling Sam, Cas knows that there isn’t exactly a way he can get past this when Sam starts asking questions.

He’s both excited and deadly terrified.

Cas has to get Dean back and save Sam and try to talk some sense into his fallen angel of a brother, but here he is, locked up and unable to do anything.

Then Sam realizes it’s Lucifer and Cas is straining to listen, wishing to be able to take control again, to warn him. Lucifer talks and Cas listens and suddenly, his grace is flaring up the way it does when he touches a soul and he feels _charged_ , ready to go and smite a few demons.

To take back control.

So he does.

Cas breaks out of the shackles, his strength back, fresh and clear and it feels beautiful. He breaks out of the dream and immediately, he is back in charge, Lucifer himself locked in the room.

Cas can feel him pounding against the doors, trying to escape, and he knows that he doesn’t have much time.

He warns Sam, straining to keep Lucifer’s grace at bay, recessive and locked away.

Cas doesn’t have much time.

But he has to save Dean.

*****

Cas uses Lucifer’s grace, teleporting to the German vessel after he speaks with Sam.

In real time, he is only there for a mere few seconds.

But combined with his newfound energy and power, Cas stands there for minutes, staring at the bright light emitting from the woman and then the man in front of him, his heart twisting and his grace thrumming inside of him. He can’t see his face, but Cas doesn’t doubt the horror and self-loathing that is slugging through Dean’s thoughts and the pain he is feeling.

Cas allows himself to look, allows himself to wish for something that could never happen. The man he fell in love is in pain and if he only knew what was coming.

Cas grips Dean’s shoulder tightly and it could be the last conscious move he makes and if only he could have warned them both.

Then he is teleporting and Lucifer breaks out of the room, wrenching Cas from control with a yell. Cas falls to the floor of the room and he can’t hear anything happening outside of his vessel.

He wants to scream.

*****

“You _foul_ creature!” Lucifer shrieks, throwing Cas across the room, his back hitting the base of the black throne.

He coughs up blood onto the pristine white tile, something erupting in his chest and making his grace feel like it is being ripped apart. “You snarky little pig! You ruined _everything_!” Lucifer bellows, throwing his hands up into the air.

Cas shivers as he tries to get up, but Lucifer grabs him by the scruff of his neck, yanking him down the step and over to the wooden chair. “I knew you loved that stupid little human, but _this_!? This is a whole new level of utterly sick obsession, Castiel.”

Not speaking, Cas moans in pain, his head smacking against the back of the chair roughly, making his ears ring. “I knew I should have locked you up tighter, angel.” Lucifer’s voice is deep now, not as loud, but deadly and it causes Cas to whimper. “How would you like to be pushed down into the dark crevices of your pathetic little mind, Castiel? How would you like to slowly become insane due to your own suffering and sorrow?”

Lucifer gets close to Cas’ face, his eyes full of rage. “How would you like to feel how I felt down in that damn cage for thousands of years?”

Cas can’t help shaking his head violently. His grace feels like it might explode and the darkness of Lucifer’s own is almost unbearable and _he wants to give up, he wants to give up…_

“But before we do that…” Lucifer grabs his hair and yanks his head up, forcing Cas to look up into his eyes. “I’m going to show you what it feels like to lose the only people that you care about in the world.”

Castiel screams and Lucifer laughs and everything goes dark.

*****

Cas isn’t inside of the room anymore.

He is conscious, seeing through his vessel’s eyes, able to feel and hear. But he can’t move. Lucifer is still in control, forcing Cas to watch as he transports them back from the depths and into Hell’s throne room.

Crowley is back in his cage, his voice muffled, but Lucifer ignores him and instead speaks to Cas slowly, a smirk on his lips. “Dear me, Castiel,” he says out loud, walking over to the throne. “What should we do first, huh? Wreak havoc upon my adversaries? Play with the doggy? Or, maybe…”

Lucifer chuckles and before Cas can protest, the devil calls in a few demons, barking strict orders and sending them off just as quickly.

_They won’t be able to capture him. Dean will know they are coming,_ Cas spats.

“Maybe…” Lucifer taps his chin and smiles. “I guess we will have to wait and see, dear brother.”

*****

Cas cries out as the doors of Hell’s throne room swing open and the demons rush in, pulling someone behind them.

“Get the hell off of me!” Dean yells, yanking back and forth, trying to escape from the demons’ grasps, but they have a strong hold on him and he is incapacitated.

Lucifer tilts his head, smiling slightly, leaning back into the throne. They both watch as Dean is dragged forward cursing and grimacing, the demons pushing him roughly. “Well, look who the cat dragged in,” Lucifer drawls, making his voice light and airy, like he isn’t about to do something dastardly which Cas wouldn’t put behind him. No matter how much Cas loves Dean, Lucifer won’t give him mercy.

And Cas is scared for them both.

Dean avoids Lucifer’s eyes, keeping his head low as he’s forced onto his knees at the base of the steps. Lucifer examines him slowly, chin propped up by a fist, eyes running over Dean’s body with something so lustful it makes Cas growl.

**He really is delicious, isn’t he Castiel?**

Cas grits his teeth and shakes with anger.

“Leave,” Lucifer dismisses suddenly, waving towards the door.

The demons immediately let go of Dean, backing away and leaving with the loud sound of the heavy doors shutting. Dean’s hands are strung behind his back and he won’t lift his bowed head and Cas is glad he doesn’t. But Lucifer chuckles lightly, uncrossing his legs and leaning forward with his elbows on his knees.

“What’s wrong, Dean?” Lucifer asks, eyebrows scrunching up in amusement.

Dean is breathing deeply, but he doesn’t answer.

Lucifer sighs heavily, standing up with a sort of elegance, slowly descending the steps until he stops right in front of Dean’s hunched figure. Crouching down, Lucifer reaches out and skims his fingers over Dean’s forehead, smiling much too softly to be real fondness.

Dean tenses up and Cas grumbles angrily, even though he has always desired to touch Dean’s face like this. But this is Lucifer and Dean knows it too, shuddering under his touch. Lucifer’s hand trails into Dean’s hair before gripping just a little too tight to be kind, yanking Dean’s head up so that he is coerced into looking up into Lucifer’s eyes, Cas’ eyes.

What they see is fear in those light green eyes, a false pretext of hate and Lucifer can also detect the desperation behind it all and Dean’s urgency to not melt under the blue gaze. “Hi,” Lucifer says softly, his head tilting again as he stares down at Dean with an adoring smile.

Dean swallows thickly, tearing his eyes away. “Get the hell away from me,” he says.

“That’s no way to talk to the King of Hell,” Lucifer says sadly, leaning closer. “And seeing how little Castiel is in here with me, I’d expect a little more kindness in that tone of yours.”

Dean doesn’t say anything and Cas can feel Lucifer becoming irritated again, growling under his breath in annoyance.

He goes for a different tactic.

Dean yelps as Lucifer stands, gripping the front of Dean’s shirt and throwing him into the air with no hesitation. He hits a pillar, collapsing onto the floor with a cry of pain, groaning as he clutches his stomach and Cas yells, his anger rising to a boiling point. “Can it, Castiel,” Lucifer says out loud, pushing Cas’ stance back with his grace aggressively. “I won’t kill your human.”

“Maybe you should,” Dean says from the ground, shaking as he lifts his head to look grimly at Lucifer.

“And risk Castiel exploding from pent up passion? I think I’ll pass on that one, sweetheart.”

Lucifer strides over slowly, a complacent look passing over his face. He grabs Dean by his shirt again, lifting him up without any strain and pressing his back against the pillar. Another groan escapes from Dean’s mouth, his face scrunching up in pain. “What does my little brother see in you, Dean Winchester?” Lucifer asks, hand gripping Dean’s throat, tight but not constricting.

Dean struggles, hand clamping down on Lucifer’s wrist. Cas is yelling, begging Lucifer to not hurt him, to not tell Dean something that could ruin it all. But he shuts Cas down, either not caring or not listening.

“He’s screaming in here, you know,” Lucifer taunts quietly, thumb rubbing over Dean’s chin. He loosens his grip and Dean chokes, heaving in. “He’s begging me to stop, Dean. And I wonder why, because… What have you ever done for him?” Lucifer lets Dean go suddenly and the hunter slips to the ground, his head bumping against the pillar. “Time after time, let down after let down… You put him down and tell him you don’t care, that nobody cares and he _still_ runs back to you!” Lucifer shakes his head in false sympathy. “So how in the world did my little brother fall in love with _you_ , Dean?”

Dean’s eyes snap open and Cas feels his blood run cold.

No. He wouldn’t…

“ _God_ , as if it weren’t clear!” Lucifer chuckles and bends down, caressing Dean’s chin to keep his head back, the expanse of his neck open and vulnerable. “Are you really that oblivious? Or do you just try and deny it? It really is a mystery that I wouldn’t mind solving…”

Cas pounds his fists against something in the dark, but then he finally realizes- It’s a door.

“Stop,” Dean pleads, shaking his head and breathing quickly.

“After everything he’s done for you,” Lucifer continues, dropping to knees slowly and moving Dean’s legs so he can fit between them. “After all of the messes he’s cleaned up, the years of wiping the drool from your chin…” Lucifer laughs, biting his lip and forcing Dean to look at him with his angelic power. “And you deny the only feeling little Castiel has ever given freely? Now that is just _cold_.”

Dean whimpers as Lucifer shuffles forward, hand grasping Dean’s thigh, and Cas gasps suddenly, feeling how close they are to Dean and his leathery scent, hearing the soft breaths he takes through his nose. “Even I haven’t fallen that hard, Dean,” Lucifer whispers, edging nearer to Dean’s face, his parted lips and his whimpers. “Even I didn’t fall in love with a human so broken that there’s no one left to pick up the pieces.”

“I-”

“Shh, shh,” Lucifer murmurs with a light laugh, hand spreading over Dean’s warm cheek. “Do you love him too Dean? Or am I supposed to believe that you feel nothing at all?”

Dean shakes his head slowly and Cas breathes in sharply when Dean’s hand grips the lapel of his suit jacket, pulling his chest flush with Dean’s. Suddenly, Cas feels like he isn’t being tugged into submission any longer and his grace is free to move about, no longer boiling in Lucifer’s drenching heat. He flexes his fingers and almost laughs.

He can move, so he does.

“Cas, please,” Dean breathes, head lolling as Cas pushes forward and presses an urgent kiss to his neck, fingers drifting into his hair and over his face.

“Please what?” Cas asks, voice light and succumbing and he feels warm all over with Dean close like this.

“You have to cast him out, Cas,” Dean whispers into his ear.

Cas tenses, remembering that this wasn’t how it started out.

And then he realizes that Lucifer is quiet and somewhere inside the veseel, hiding in the dark. Cas wonders if whether he consented to letting Cas take control or…

If he was forced to.

“Did you…” Cas starts, leaning back, blinking rapidly.

Dean nods and holds up his trembling hand. His fingers are smeared with blood and a green powder and Cas glances down, staring at the angel suppressing sigil painted in the thin film of dust lining the floor. Immediately, Cas throws his arms around Dean’s shoulders, hugging him tightly and shuddering at the regain of control and sudden flood of emotion. “I’m so sorry,” Cas whispers, squeezing Dean’s head lightly and closing his eyes.

Dean’s arms circle his waist and Cas collapses into his embrace. “Fuck, Cas, why the hell did you say yes?”

“I wanted to be of use,” Cas answers honestly, too tired and afraid to tell a pitiful lie.

“You are of use, man.” Dean leans back and cups Cas’ cheeks softly. “You’re a hero.”

“I’m just a hammer, Dean. I’m expendable and we need Lucifer to stop Amara.” Cas looks up into eyes flecked with green, the fear from earlier having melted away and leaving the warmth and kindness. “I can’t expel him.”

“To hell with Lucifer, Cas!” Dean’s voice is urgent. “It isn’t worth it. You’re not worth losing.”

“I-”

“Dammit, Cas, no! Whoever said you were expendable clearly doesn’t understand what we’ve been through or how you’ve risked everything to save the world when I couldn’t. We’ll find a way, Cas. Even if it means searching the whole universe for freaking God and the archangels.”

Cas exhales, looking at Dean and back at the sigil.

“Please, Cas. Just say no.”

Dean looks into his eyes and Cas is about to open his mouth and give his answer when Lucifer wrenches inside of him, his grace unfurling and spreading throughout Cas with a villainous stab of fury. Gasping in pain, Cas hunches over with his hands on either side of Dean’s legs, dropping his head low.

“Cas, you have to cast him out!” Dean yells, gripping his shoulders.

Cas groans as his head starts to swim, Lucifer screaming ferociously into his ear, and then he decides.

“Get the hell out of me,” he says sternly, shuddering as Lucifer suddenly stops and his grace is released.

Then there is a horrible pulling sensation and Lucifer is pleading for Cas to take him back, but he can’t do it again.

They’ll save the world and defeat the Darkness without him.

A bright light flashes through the room and Cas finally feels the fiery, corrupt grace being yanked from his own, from his body, and then he collapses into Dean’s open arms, slipping into unconsciousness.

*****

“Cas, buddy, wake up.”

Cas hears Dean’s voice, feels his warm hands cupping his face. It feels nice, amazing in comparison to the cold drafts Cas had been enduring for a few months. Now if he could just slip away again…

“Please, Cas.”

He blinks his eyes open, breathing heavily as he looks up at the beautiful face of Dean Winchester, everything suddenly coming back.

“Is… Is he gone?” Cas asks slowly, turning his head to look around the room.

“Yeah,” Dean breathes out, smiling. “He’s gone, Cas.”

Cas sits up slowly, pressing a hand against his chest. He feels so much better without the constant flutter of evil and Lucifer’s haunting voice. It’s the best relief he’s felt in a long time and Cas regrets ever treating possession lightly, without any sorrow for the vessel. Dean’s hands are still constant on him, patting him on the shoulder and the face and his leg. “Thank you, D-,” Cas says.

“Shut the fuck up.”

Suddenly, Dean is gripping Cas by the lapel of his suit jacket and kissing him soundly, shutting him up with the best solution Cas can think of. Cas is thoroughly surprised at first, his eyes still open, but when Dean grumbles something on his lips they pull apart. “What the hell are you doing?” Dean demands, sort of laughing while also looking pissed off.

“What- what do you mean?”

“Kiss back, you idiot.”

“R-right.”

Cas cups Dean’s face and they come together again and this time, their lips are needy and kisses hungry. And they’re sort of at an awkward angle and Cas can’t even think a coherent thought, but this is everything.

And then so much more.

*****

“Dean!” Sam whips out his gun and points it at Cas’ chest, huffing angrily in confusion, his eyes wild.

“Sammy, calm down,” Dean says, putting his hand up. “It’s Cas.”

“How do you know!?”

“I cast Lucifer out,” Cas explains, leaning against Dean tiredly.

Even after the spark and electricity that ran through his body when they kissed, Cas feels worn out. He could actually use a few hours, or, maybe days, of sleep.

“You did?” Sam asks.

Both Dean and Cas nod and Sam lowers the gun, a relieved smile replacing his angry frown. “Dammit, Cas, it’s good to have you back. But-”

“Hey, let’s save the lecture for tomorrow,” Dean cuts in. “It really took a lot out of him.”

“I do think I need to rest for a while,” Cas says, rubbing his eye with a loose fist.

“Right, right,” Sam says. “You’re room is still set up so if you want-”

“Uh, no.”

They both look at Dean who shrinks under their confused gazes, biting his lip. “Cas is uh… Cas is gonna sleep in my room.”

Sam smiles awkwardly. “But Cas has a room, Dean.”

“I know. But why would he sleep in there when…”

Sam waits, looking at Cas with scrunched eyebrows. “When what?”

“I think Dean is trying to say that I would rather not sleep alone tonight,” Cas says gently, gripping Dean’s coat. “Or really, never again.”

Sam looks sort of creepy with that strange smile on his face and Dean groans. “ _Sam_. Cas is sleeping in my room, in my bed, with _me_.”

A warmth runs through Cas’ body, a beautiful contrast to Lucifer’s icy grace and he looks at Dean fondly.

Sam’s mouth drops open and he nods slowly, looking back and forth at Dean and Cas. “Oh! Oh. Oh…”

“Yeah.”

“Oh, um, okay. Cool. Yeah, of course. Wait, how-”

“Another day, Sammy!’ Dean interrupts loudly, grabbing Cas’ arm and pulling him towards the hallway. “Another day.”

Cas chuckles and Dean gives him a look. “I swear… Sam is freaking clueless.”

“It was a bit surprising, Dean.”

Dean stops and gazes at Cas with something Cas can’t quite make out. “Took me long enough, huh?” He finally says softly.

A smile slowly spreads over Cas’ face and Dean leans in close, tipping Cas’ chin up with his fingertips.

“At least it wasn’t too late, Dean,” Cas whispers against his mouth and Dean agrees by pressing their lips together softly.

Not too bad, huh?

 

\- Chuck 1:60-78


End file.
